To raise the heat efficiency, it is effective to raise the mechanical compression ratio ((top dead center cylinder volume+stroke volume)/top dead center cylinder volume) to raise the expansion ratio. However, if raising the mechanical compression ratio at the time of engine high load, the temperature and pressure inside of the cylinders at the ignition timing rise, so knocking easily occurs. Due to this, it is preferable to raise the mechanical compression ratio only at the time of engine low load operation where knocking is hard to occur. For this, it is known to make the cylinder block and the crankcase move relatively to each other to change the distance between the cylinder block and the crankshaft so as to make the mechanical compression ratio variable.
In a V-type internal combustion engine, it has been proposed to make the cylinder block parts of the two cylinder groups move relatively to the crankcase separately along the cylinder centerlines of the cylinder groups, but it is difficult to make different cylinder block parts move relatively to the crankcase by a single link mechanism (or cam mechanism). A pair of link mechanisms (or cam mechanisms) becomes necessary for each cylinder block part, so overall two pairs of link mechanisms end up becoming necessary.
To reduce the number of link mechanisms, a variable compression ratio V-type internal combustion engine has been proposed which joins the cylinder blocks of two cylinder groups and makes the joined cylinder block move relatively to the crankcase by a pair of link mechanisms (refer to Japanese Unexamined Patent Publication No. 2005-113743).